// set 也可以用数组的解构赋值
let [x,y,z] = new Set([a,b,c]);
// iterator 接口
function* fibs() {
    let a = 0;
    let b = 1;
    while (true) {
      yield a;
      [a, b] = [b, a + b];
    }
  }
  
  let [first, second, third, fourth, fifth, sixth] = fibs();
  console.log(sixth)// 5